The present invention relates to an isopleth generator for applying isopleths or contour lines to digital image data, and a method therefor.
When observed data of temperature distribution, pressure distribution, etc., or two-dimensional distribution data such as a simulation result of those observed data by means of a computer is displayed on a display, generally, such data is expressed by variable density of picture elements, change of hue, etc.
In consideration of making observation easy, accurate, and so on, it is more convenient to add isopleths or contour lines obtained by successively connecting values of the same level.
As an example of a conventional isopleth generator, JP-A-1-187678 discloses an isopleth generator in which isopleths made up from measured data by successively connecting data of the same level can be drawn smoothly.
In this example, isopleths are displayed in the following manner.
The isopleth generator is provided which a first memory holding original image data of one frame or more, and second and third memories each having a memory capacity for storing image data of one frame, so that data read from the first memory is binary-coded on the basis of a predetermined threshold value and the binary-coded data is stored in the second memory.
Further, the data in this second memory is processed so as to be expanded or contracted by one picture element, and the thus processed data is stored in the third memory.
A difference between the data in the second memory and the data in the third memory, so that only the portions corresponding to isopleths becomes data having values other than zero, while other portions become data having the value zero. Thus, isopleths or contour lines can be obtained and displayed.
In the above-mentioned conventional example, in order to make up isopleths, memories each having a capacity of (1 bit).times.(1 frame) are required by two in number as the above-mentioned second and third memories.
In addition, since it takes much time for these memories to execute read/write operation (overhead) of data, the conventional isopleth generator has not been suitable for dealing with animation or the like in which the image data changes every frame.